"Power factor correction" (PFC) techniques are used to realize AC-to-DC power converters which draw input currents having low harmonic content. For additional background, see the patent application entitled "LOW COST AC-TO-DC CONVERTER HAVING INPUT CURRENT WITH REDUCED HARMONICS", U.S. Ser. No. 08/543,561, filed Oct. 16, 1995, by Francis M. S. Ho, et al. (the subject matter of which is incorporated herein by reference) and U.S. Pat. No. 5,446,366 entitled "BOOST CONVERTER POWER SUPPLY WITH REDUCED LOSSES, CONTROL CIRCUIT AND METHOD THEREFOR", issued Aug. 29, 1995, by John A. Bassett, et al. (the subject matter of which is incorporated herein by reference).
FIG. 1 is a simplified circuit diagram of an AC-to-DC power converter 1 designed to have low input current harmonics. AC-to-DC power converter 1 includes input terminals 2, a rectifier bridge 3, a power switch 4, a storage capacitor 5, one magnetic component 6 (having a first primary winding 6A, a second primary winding 6B and a secondary winding 6C), power diodes 7, 8, 9, an output rectifier circuit 10, a control circuit 11, and output terminals 12.
First, although such AC-to-DC power converters operate satisfactorily for many applications, it is desirable to reduce the number of circuit components in order to reduce cost. Second, although the input current harmonics of the AC-to-DC power converter of FIG. 1 are relatively low, it is nevertheless desirable to reduce such input current harmonics further. FIG. 2 is a waveform diagram illustrating the input voltage and input current waveforms of the AC-to-DC converter of FIG. 1. The sharp current spikes of the input current waveform represent undesirable high frequency input current components.
Accordingly, an AC-to-DC power converter is desired which has improved input current harmonics and which also has fewer circuit components.